As part of the partnership between Library and Archives Canada and Canadiana.org various microfilms held by Library and Archives Canada have been digitized and placed online on the Hertiage site for all to peruse. See the latest announcement at the LAC blog.
Several of the microfilms that have been digitized contain the parish registers and township books for places across Canada. To see a list of these collections you can search for "parish registers" on the Heritage site. Under each collection set there is a count of the number of microfilms that have been digitized.
To find out what is on each microfilm you need to click the "About" tab after you click on the "Reel ID".
Unfortunately the descriptions of what is on each microfilm is very brief and usually only from the first record set ... and there may be MANY record sets on a single microfilms. Additionally, some of the microfilms are misfiled in the wrong collection which just aggravates the issue. This makes it a challenge to know if the parish register you are looking for is in the collection or not.
For example, on microfilm H-1812 in the Manitoba Parish Registers collection the About tab states, "Holy Ghost Parish fonds [Winnipeg, Man.]". But if you go to the end of that film you will come across "SIMS, Rev. Jabez (1831-1869). Church of England Missionary" which is Shelley Pearen's biographical sketch of Rev. Jabez Sims that includes a hand drawn picture of his family tree.
Hopefully, one day, the Parish Registers finding aid book that is on the shelf on the second floor at the Library and Archives Canada building at 395 Wellington Street will be digitized and the searching will be made just a little bit easier.