CadVistor said:
Yes, I have already digested that page. My question is how difficult is it to get an extension and how many extensions can you get in a row.
All depends on the specific case:
Are your parents from a visa except country, do they have lots of ties back to their own country, what is their travel history like, what are the reasons for the visit, can they support themselves, will you support them, can your parents make good case that they will leave Canada.
If you meet all the conditions shown at the web page then it is easy to get an extension, the less convincing your case, the less likely a positive outcome.
I know of a few people who have extended for a total of three of four years. I have been issued multiple extensions (four VR's if I remember correctly).
How long do you want your parents to stay in Canada?
Have you applied to sponsor your parents?