Where do I cash in about 100.00 worth of canadian coins around the mt vernon wa area

You're so close, take a drive over the border and spend them. ;)

Er... seriously. How about the bank?

Go to this site, they exchange Canadian Coin for US dollars. http://sites.google.com/site/wsbcce/

WSB Canadian Coin Exchange

Any normal US bank will exchange them.

Also most stores will merely accept Canadian coins in small amounts