Travel Canada advice

Hi all. I live in Toronto/Ottawa. My nephew (17 year old) is visiting from Denmark for about 3 weeks in June/July, and my husband and I (35 year olds) are thinking of doing some kind of a road trip with him. He is very much into swimming, fishing, diving. Our two main options are doing a road trip towards the East Coast (Nova Scotia and PEI) or Northern Ontario? Another option could also be able to explore Quebec more.

He has already been to BC but swimming was not an option because of the cold water even during the summer. I have been to East Coast in 2019, had a good time.

What would you recommend? Feel free to suggest ideas outside of the options I’m laying out.

Thanks in advance!