Father/Son trip to Alaska or the Grand Canyon

I went to the Grand Canyon last summer with my son who just graduated high school.  It was fun and not overwhelming.  It's really different from Northern California which is nice.  It's a crowded national park so it's not disorienting.  The Grand Canyon is awe inspiring.  I'm not too adventuresome, so we did short walks and hikes, had ice cream somedays.  All very innocent fun.  On the other hand, I would think now is the time to see Alaska, because of global warming. 

Alaska, hands down. The Grand Canyon is way too hot in summer.

Although there is a difference in generations between your proposed trip and what our family experienced, I can wholeheartedly recommend Road Scholar. My 82yo Dad took my 16yo son to Italy and my 11yo son to Safari West in Sonoma with Road Scholar this summer as part of their Grandparent/Grandchild(ren) trips, and both were extremely well organized and all family members had a really good time. Road Scholars also offers Family Trips, which would probably be perfect for your husband and son.

I just came back from a charter trip down the colorado through the Grand Canyon. While it is hot there during the summer, you have the river to cool off - not a problem. Also, in August there are often afternoon showers that cool off the canyons wonderfully. We went with Canyon Explorations. I believe they only run non-motorized boats and that is a huge plus. You really get a feel for the canyon sounds and the water without motors. We camped for all 14 days on the river. the guides did all the set up, cooking, and boat guiding. they also took us on hikes (optional) and had a lot of knowledge of the geology, flora, fauna and human history. They had a "library" of books you could borrow to read on the trip. The company provides sleeping bags, pads, tarps and sleeping bag liners (most nights are too hot to zip up in a bag). they also provided tents to those who wanted them. it was gorgeous and amazing and so very worth it. depending on how much time and money you have, you can take shorter trips and hike in or out at about the halfway point at Phantom Ranch (I like the eastern stretch more the the scenery is amazing in any case).  Anyway, I would highly recommend GC with Can Ex for a post-highschool trip. 

If you decide on Alaska, you might check out Cheena Hot Springs. Also, there is a ferry that you can take from Bellingham WA to Alaska (not sure where) and you can take your car on the ferry if you want to make it a road trip