The field of view will be considerably wider on the E-PL1 w/ the 20mm than with the T1i w/ the 50mm. Using the standard 35mm equivalence*, the 20mm on :43: is a 40mm equivalent (40mm x 2.0CF), while the 50mm on the APS-C from Canon is an 80mm equivalent (50mm x 1.6CF). Another way to put it would be that the 20mm on the :43: will have the same FOV as a 25mm on the Canon.
* equivalence gives the focal length on a 35mm/full-frame camera that would yield the same FOV as a way to standardize across sensor sizes. It's not actually a longer focal length, but rather a smaller crop of the same image due to the smaller sensor that yields a similar FOV as a longer focal length would on the larger sensor.