Hello MaureenNC, and welcome to Cruise-Chat;
Princess and Holland America have a good reputation for their Alaska cruises. Of the two, I think Princess would have more to offer your girls. However, in the Caribbean, RCI (Royal Caribbean) might be a better fit for a family with young children--especially their larger ships.
I am amazed at the variety of activities available in the Alaskan ports now; I can't imagine anybody not finding activities to suit their interests.
If you are not doing a land tour, I think the round trip from Vancouver or Seattle, or even San Francisco is a good choice. You have more opportunities to see wildlife in the Inside Passage than you do crossing the Gulf.
Seeing wildlife from the ship is always a matter of being in the right place at the right time; but yes, I have seen everything you mentioned, and much more from the deck of a ship. And there are wildlife excursions available in the ports--you don't have to do a land tour to see wildlife.
I think any Caribbean ports are good for kids; for the most part, the ships avoid the ones that should be avoided. Kids love the water and the beaches and that's what the Caribbean is all about :-)
As for the weather in Alaska, it is also hit and miss, like wildlife sightings. Having said that, July is probably your best opportunity for good weather. But you need to always be prepared of cold and drizzle.
My I say something here from my heart? I can tell you want very much to see Alaska; and it would be a wonderful adventure for your girls. But if your husband had a negative experience on his first cruise to Canada, and if you in fact feel this may be your "last chance to sell him on the cruise concept", maybe you should consider the Caribbean; children are happy anywhere, and isn't the family being together the most important thing anyway? Reel him in on a nice Caribbean cruise; Alaska will always be there--in spite of what the global warming people tell us!