Best time to visit Eastern Canada

[Happy_Harry]

Would like to do road trip in Eastern Canada plus NE USA ( NYC). Am thinking of June/July time frame. It seems if you go early/mid June flights etc are significantly cheaper than end June/start July.
I was wondering if the weather is significantly different(worse) in the start/middle of June than start of July, and when there would be more mosquitoes ( the better half doesn't appreciate them).
Route would roughly be NYC, Toronto, Niagara Falls, Montreal, Halifax, starting in any of these, it is a round trip start point will be decided on either weather or where I can fly to/hire car cheapest.

 

[leafs]

July would be warmer but June is usually nice also. I would recommend mid june. Elementary schools finish at the end of June in Canada so less families travelling.
New York and then Niagara Falls on way to Toronto. Then take Highway 401 towards Montreal. I did a trip out east in 90's. We went over US border and drove through Vermont and Maine., stunning. New Brunswick not much to talk about, keep driving. Stay in Halifax. Take Ferry over to Prince Edward Island (small Island, not much to do but chill). Back on mainland make sure you do the Cape Breton tour around the coast. Reminds me of Ireland. I remember it was a lot of driving and we were tired so make sure you break it up.