Dual citizenship minor travelling from USA to Canada

My 14 year old child will be travelling alone from the US to Canada this summer.
My child has a canadian and a us passports, is it best to travel with us or canadian passport? I will be asking my sister in Canada to get an insurance card for my child. Would my child have problems coming back to the US at the end of the summer with both passports on hand.

I have dual citizenship, my child was born in teh US.

Thank you for your advice

Use both passports:

-enter Canada on Cdn passport
-enter US on US passport

Note: most provinces have a wait time before provincial health coverage begins......so its best to ensure and obtain private coverage before provincial coverage begins.....

Thank you for your advice
My child will be covered under my Health plan, I will get additional coverage in Quebec.