Unfortunately you can not use Google Earth Streetview to look at most of the sites in Tunnel Mountain any more. It used to be the best way to figure out which site you wanted and how it sat in comparison to the others around it. You can still get in to some of the sites and also on the periphery of the campground so you can look in and see if camping like that is your cup of tea or not. The trailer park and village 2 have nice views of the mountains (and your neighbors).
There are three different areas in Tunnel Mountain - the trailer park, village 1 and village 2.
Tunnel Mountain Trailer park (the main part of the campground for trailers) is basically just paved roads with pull offs to the side where you park. There are full hookups in all of it, but don't expect much in the way of privacy. No fires (even propane) are allowed. No Google Earth Streetview.
Village 2 is similar to the trailer park but it is not fully serviced and a few sites allow fires. No Google Earth Streetview.
Village 1 is more of a true "camping in the trees experience". Fires are allowed but there are no hookups. The sites are more "conventional" but smaller so be mindful of that if you are booking. You can still look at the sites in Streetview.
There can still be snow in Mid May. Usually, Sunshine Village ski hill is open until the Canadian May long weekend and a few people I know take the opportunity to camp and ski. Most of the snow in Banff is typically gone by then.