Most cameras now let you see the contents of the memory card by displaying the card as a disk drive.
This is convenient but is a handicap for a full featured camera.
The T3i used a driver which lets people write programs to operate the camera remotely from a computer.
To download the photos to your computer you must use the software provided by Canon (EOS Utility).
If you want to view the contents of the card easily, you must buy a card reader for your computer.
Put the memory card in the card reader and you will see it as a hard drive.
When you loaded the Canon software it changed your program affiliation.
I do not know how to change your program affiliation back to "iphoto"
With my Sony DSC-R1 camera, when I plugged it into my computer the memory card showed up as a drive.