Did you download Windows 7 driver
for the printer? I'm not familiar with Cannon but Epson many times have USB driver in firmware. On my printer it won't share unless it's connected to the Vista machine(I have 2 PCs, one Vista one Windows 7)
In my case there is no downloadable Windows 7 driver. The one in firmware is it. But I looked up yours and it claims to have both 32 and 64 bit Windows 7 drivers
: Canon U.S.A. : Support & Drivers : PIXMA MP210
In my case when the printer was connected to Windows 7 machine, I could see it from Vista but the Icon was not correct and it didn't work. The printer driver has to serve itself over the network or it won't work right.
Also you don't say your Service Pack level. If Vista before SP1 you need to create a virtual port. The same trick that was used on OS/2 back in the 90s. If SP1 or later then it should work with the right driver.