I have a US based Cingular, and will be traveling to Canada. Will I still be able to get and send PINs to US phones?

PIN messaging is PIN to PIN via RIM's own network, it does not matter where in the world you find yourself.

Great, thanks.
For email when I'm in Canada, will I still get them? If I don't actaully open the email, will I still get hit with large roaming or out-of-plan data charges?

Yes, you're charged data roaming. As messages appear on your Blackberry you're charged data - regardless of if you open them or not. I'm Canadian and regularly travel to the US. Most carriers have roaming agreements but the safest bet would be to contact your carrier to find out.