Archives of Ontario provide explanations of what is included in their vital statistics provision for Ontario.
There are two series of microfilms. The first series is the index (sorted by surname and year) and the second contains the original registers with registration numbers that correspond to references found in the index.
Microfilms may be ordered in Canada from Archives of Ontario through inter-library loan. They use their own series of microfilm numbers. Elsewhere, microfilms may be ordered through the nearest Family History Center. The Ontario Archive microfilm numbers can be found on their website and they also include a conversion list to FamilySearch microfilm numbers. Ancestry or Ancestry Canada provide images direct from thei own index (but not without paying a subscription).
FamilySearch do not provide microfilm images online but have a very good index online.