Middle of Summer - things are going to be crowded, especially on the roads, and a bit pricey. You should get booking as soon as possible.
Canada is huge, and diverse as Australia so it will be best to choose an experience type and confine yourself to one, maybe 2 areas.
The 'Maritimes' - New Brunswick, Prince Edward Island (PEI), Nova Scotia and Nova Scotia - are very pretty, quaint and scenic; sort of a New Zealand or Tasmania vibe. Nova Scotia would be the pick of the bunch, in my experience for 2-3 days. Great place to see moose and the occasional bear. You could even venture into coastal Maine. If you like crayfish (lobster) this is the place for you. just ask drron and mrs.dr.ron (see their trip reports).
Churchill in Northern Manitoba is the place to
see polar bears, but summer isn't the best time. there's at least one Trip Report on AFF about the bears at Churchill. I don't think summer would be a good use of your time.
Undoubtedly the best part of Canada in summer is the Rocky Mountains. For an almost first timer, this would be my choice and 5-7 days is a good period of time. the 'classic' itinerary is to take the Rocky Mountaineer train from Vancouver to Jasper, then drive down the Icefields Parkway to Banff and Lake Louise, and then to Calgary and fly out. I would definitely recommend looking at adding, from Banff, to drive down Highway 93 to radium Hot Springs (very scenic, very high chance of seeing bears on the road side), then up H95 to Golden, then head back east on Highway 1. That might be a bit too much driving, though, especially with the crowded roads in summer.
Another alternative would be, at Banff, take Highway 1 all the way back to Vancouver. Bears are less common along Highway 1 and the opportunities to pull over and observe them are limited.
The Icefields Parkway and Highway 1 in the Rockies are amazing, with many walks and scenic points.
if you really wanted to see bears, Alaska is the place! I went to Brooks Falls for just 2 days (see trip report in the footer) but there are heaps of other places. See
here for example. Obviously research this carefully, with respect to timing. if you go too early, and the salmon are late, the bears won't be active or numerous (but you will still see them). It'll cost ya.
Happy to fill in more detail on particular areas.