http://www.ppt.gc.ca/menu_e.asp
Check here. Although it's not manditory, it is your best option. Without it you will require at least two pieces of ID with your picture on it and if you are flying into the States, Customs can get real picky.

First you get your pic taken at some place that takes them...they have to be a certain size. Then you fill out an application...and you need witnesses....you take the application and the photo along with two other pieces of ID (birth certificate, etc). Then it usually takes about 4 weeks.

I see that there is now an on-line application form. You might want to check that out.