USA to Canada and back postage question

[tolpine]

Hi, I'm new to the autograph collecting hobby and henceforth, this is my first letter that I will be sending out.
I have the address all ready to go, along with my letter, picture for if they fill my request to autograph, and the SASE.
However, I'm a bit confused on the postage.
Going from the United States to Toronto, Canada-Do I use USA postage stamps or Canadian?
Vice versa,for the SASE envelope-Do I use USA postage or Canadian postage?
Also:
Since it's going to and from Canada do I also need to include IRC's? If so how many do you think?-It's a 12x9 inch envelope.
Thanks!:D

[RYAN-J]

Not sure if you've sent your letter out yet, but when I send to Canada, I take my main envelope to the post office and they weight it and put postage on it. for something 9x12, it's going to cost around $5.00. for return postage, I simply send a SAE and a couple dollars, so they can purchase canadian postage to put on the SAE.

RYAN-J