Yes, better to have a couple cards than one big one in case of failure.
Canon recommends a class 6 card minimum, but class 10 is still cheap and doesn't hurt to have a card that is capable of more speed than the camera. Some of the manufacturers are now rating their cards in "x speeds", like "133x", these are capable of speeds in excess of the class ratings.
Example: A pair of Lexar Pro 8GB "133x" cards (they guarantee 20 mega bytes per second performance from these cards) is only $48 on Amazon.
I believe the T3 write speed is rated at 45 Mbps (mega bits per second) which is just shy of 6 MBps (mega bytes per second). Of course that speed will vary in camera.
The "class" rating is the sustained speed performance of the card in mega bytes per second, so a class 6 card will maintain sustained speed of 6 MBps, class 10 = 10MBps...so, technically the Lexar cards mentioned above are "class 20" cards.
Just find a good brand, class 6 or better and don't sweat it.