You should go visit your dad in the US if you really want to see each other.

My sister was in the same position as your dad and I was getting married in Canada. She had her immigration lawyer get some kind of permission letter to reenter into the US. I think death of a immediate family member and a few other "special" cases. She needed the lawyer because a wedding of her brother wasn't on the list of critical events that warrented her legal status to leave.

It was a huge pain in the a$$ for my sister. This visit sounds like dad just wants to see you. Its not worth the risk. Why don't you go visit your dad in the US?

PS - this isn't a Canadian problem its a US Immigration issue