Dude, if he's coming in the summer, no worries. It's the summer, and yes here in Alaska we get summer just like everywhere else. It's not ice and snow up here like people think year round, as a matter of fact, because we are so far north we get TONS of sun in the summer.....anywhere from 18-24 hours of sun a day! So it can get quite nice and warm because of all the sun.
If you are taking a cruise, you will be going through my region. I run a little video production company in Juneau. The SE portion of Alaska (Juneau, Ketchikan, Sitka, Skagway, Haines) is mild and doesn't even get that cold in the winter as we are right on the water. We do however get LOTS of rain, in the winter and the summer so bring a rainjacket for yourself and your camera!! Along with that we have some cloudy, misty weather so the contrast isn't always the best for shooting on those days. Of course if you get sun, you'll get some of the most beautiful shots you've ever seen! When in Juneau make sure you get out and see the glacier (you can drive right out to it, and even walk up to it if you want to take a bit of a hike from the road, you can see it really well from the visitor's center though). Other tour ideas... you might want to take the tram up to the top of the mountain to get some "arial" shots of Juneau and the surrounding area. Glacier Gardens is another nice tour (with "arial" type shots), and the Zip Line is a blast. For a more relaxed time you can check out the Juneau Steamboat Company (a real ride on an steam powered boat) and get some shots of Juneau and the boat and plane traffic in the channel.
Denali is in the interior and they have some of the nicest summers around (and coldest winters) Down here we range from 20 degrees in the winter to 75 or so in the summer. In the interior they can get down to -60 in the winter but get up to 95 or so in the summer as they don't have the ocean to moderate the temperature. I'd bet you'll have nice weather up there and get some nice shots of the mountain.
Anchorage is the big city and you'll find lots of stuff to see and do around there.
Any other questions just ask! You'll have fun, trust me!!!