Driving is very challenging on both roads, but ocean and mountain vistas are not interchangeable.

We would recommend the Red Bus Tours (google for web link as pasting URLs are not allowed on Trip Advisor answers)

Privately owned guided tours are not allowed within Glacier or any National Park. You can book Red Bus or Sun Tours...they have routes that include the Sun Road. Both those companies are concessionaires that are allowed to conduct those tours within park boundaries. Red Bus has in the past booked private tours for smaller groups or weddings etc. They do not allow us to post live links on this function...so access Red Bus tours by using Duck Duck Go or Google. Type in Glacier National park red-bus-tours and the link will appear. Or type in Glacier Sun interpretive tours. You could even contact Glacier Guides and see if they have any plans to conduct auto tours over the Going to the Sun Road this year. In the past they have only conducted hiking and biking tours...but you never know. Good luck on this. Hopefully there will be space on the tours so close to your visit.

If you have the time you can enjoy the L & C Caverns if they are open. When is your trip? The best and actually the most scenic is to make your way north to the I-90...follow it all the way to just past Missoula then take the 93 north from there to Whitefish. The section of the I-90 from the Bozeman area all the way to the Idaho Border is considered the most beautiful freeway route in America. Depending on how you leave the Tetons, the really pretty route is the 287 from West Yellowstone...or use the Idaho 87 instead heading north up through eastern Idaho to connect with the 287. Ennis is a nice place to stop on the way. Then L & C Caverns...then hit the I-90 from there. == I would not advise using the 287 to Helena and then the 141 and 83. It looks like a shorter cut across to Bigfork...but that road is not as scenic, has more 2 lane and the 83 section is known to locals as "dead deer alley". So many deer are hit that they often have to send up a special truck to collect the bodies. Hitting a deer can ruin a vacation. == If you spend a lot of time at the Caverns it's possible you may wan to overnight in Missoula at the end of the day before completing the drive to Whitefish. The 93 is a gorgeous drive too...you go up through the Mission Mountain valley and then along the west side of the huge Flathead Lake. Do you enjoy botique breweries? At Lakeside along the east side of Flathead Lake you could visit the Tamarack Brewery and grill. Beer optional...food is great too. You will enjoy Whitefish!

There are some problems you will face with your goals...having only 1 full day. Its a very long drive of over 2 hour 45 minutes normally without stops between West Glacier and Many Glacier Valley. This year, there is a 40 minute construction delay getting into MG valley from Babb and then again on the way back out. Plus if you do not have hotel or boat tour tickets for the exact day....IF they close the road for crowding or lack of parking you will not be allowed in...maybe for hours. --- The 2 hikes you list may not be melted out yet...sometimes the trails are muddy or snowy until end July even into August. If the Grinnell was melted, it takes 8 hours with the help of the 2 lake boat tours or hiker shuttles in the morning. Iceberg Lake the same. It lies in the shadow of a 3.000' cliff that keeps the ice frozen longer before the thick chunks break off and begin to float...normally by late July or August. It's also a 10 mile hike RT with over 1,700' elevation gain. Try to concentrate your day along the Going to the Sun Road and take some of the famous hikes along it. Hidden lake Overlook, the Highline or the St Mary/Virginia Falls on the east side of the GTTSR corridor. ***BUT, this year you also must obtain a ticketed entry to go onto the GTTSR. You cannot just drive in and expect to do that. You must do that on line before you come. Please...there are many things you need to know to make this a nice day for you. Go to the Glacier forum page and ask a question there. We can really help you more and give you clickable links to pages you need to see. When you get to the forum page there is also a list of Top Questions on the top right side of the page. Those are current and are excellent sources of information for you to look at. Glacier looks small but it takes time to drive through and then time to do anything. Plus Covid and the timed tickets for the GTTSR complicate things for a last minute visit. Ask your questions on the forum page we can help you more. We cannot even give clickable links on the part of the TA.

ACTUALLY, Going to the Sun Road is very unlikely to fully open until mid to late June...even into early July...depending entirely on the kind of Winter Snows we get each year. It takes months to clear the road, re-install safety barriers, repair avalanche damage or clear huge rock-falls. Sometimes the avalanches and rock falls are significant. Plows encounter trees, shrubs and even huge boulders hidden within the snows they have to clear from the road. Freeze/thaw and Spring rains also cause rock to crack, fall away and then down onto the road after the snow has been cleared. One summer, 3 cars were stranded for hours and hours between gigantic boulders on either side of them. No one was hurt that time but it took hours to blast the rocks into pieces that could be moved off of the road and down the side into the canyon below. ===== Sometimes in late Spring the Sun Road will be accessible part way to Logan Pass Summit from either side of the park earlier in the Spring/Summer but you still cannot cross over the pass for complete access because of more snow to be cleared at the top. For example cars and bikes have access for as far as its safe and then must turn around. The final thing to clear is the Big Drift just down from and heading east from Logan Pass. So what you CAN do is enjoy the Lake McDonald Valley and the GTTSR for as far as its open. Its gorgeous in late Spring and Early Summer. You can rent water craft/paddleboards to use on Lake McDonald or take rafting trips on the river from West Glacier. You can drive to Avalanche, which is north of Lake McDonald Lodge and hike the Trail of the Cedars/Avalanche Lake...its rated a moderate hike and will fill about 4 or 5 hours time...more if you stop at the lake for a picnic or just to sit and enjoy the scenery. You can drive to historic Polebridge and Bowman Lake which is slightly NE of Apgar/West Glacier. The Polebridge Mercantile is famous for its great off the grid bakery. Scenery along the drive heading up there is so pretty early in the season because of the remaining snow on the mountaintops across the river valley below. You can also spend some time in the Flathead Valley which is nearby to the west. Whitefish, Bigfork and the huge Flathead Lake are wonderful in Spring before Glacier becomes fully accessible. ===== Double check before finalizing plans...we may still be affected by the Covid edicts this year again. You may not know it...but the entire EAST side of the park was closed all of last year because of Covid and the closures it caused for all lodgings, shops, tours, Red Buses, free shuttles and lake cruises. DO Make reservations though...in case things return to near normal. Keep checking back on the Glacier Forum for updates.

It was very crowded in August this Covid year .Had to get up really early to find a parking spot at Logans pass .The hikes were really nice ,everyone was respectful ,saw quite a bit of wildlife .Weather in May might be a challenge ,it snows into the summer sometimes .Logans pass is at high elevation and very narrow so its going to depend very much on the weather that week .

Sun road was busy but manageable I would say.