Immigrate to Canada with extreme caution.

Like most other countries you can not become a citizen immediately - you are first allocated "Permanent Residence" (this status has different terms in other countries). It can take up to three years (do not believe the timeframes on the CIC website -multiply by three to get a more accurate estimate) for your application to be approved. Or rejected, of course.

Basically permanent residence is a provisional acceptance as an immigrant. Upon landing you will receive a Permanent Resident card (like a credit card) that contains all sorts of information about you in a magnetic strip and which displays your photo. The important issue is that it proclaims the date you have landed in Canada as an immigrant and gives an expiry date about five years hence. This card is used instead of a passport when you enter Canada from outside its borders and tells the immigration officer that you have the right to enter Canada. 

To renew the card after the expiry date, your permanent residence will be reconsidered. If you can prove that you have been "physically present" in Canada for 730 days in the five years, you can get the card renewed and you will be able to travel out of Canada and return. If not, you lose your residency and you are given 30 days to get out, unless you appeal the decision. Serious stuff.

Now here's the rub: the law (Immigration and Refugee Protection Regulations, Section A28) states that you can count days that you have spent physically outside of Canada IF you were in the full time employ of a Canadian company, or you accompanied a spouse who was. What you will find out after it's too late is that "full time employ" and "Canadian company" have very specific meanings in this law.

Firstly, you are regarded as employed only if you are paid a salary. Nothing else is accepted (forget it consultants and business partners, you do not qualify).

Secondly, you must have been appointed by the company at a time when you were actually physically in Canada - no other appointments are acceptable. So if you work for a company like Bell Canada in, let's say, Massachusetts USA, and you received a letter of appointment without having physically been in Canada at the time, forget it, you cannot count those days that you were employed by them.

Thirdly, the company must have been in existence for at least 2 years and must have more than five employees. That takes care of Bell Canada but there are many companies who will not qualify.

Fourth - Canada Immigration count the hours when you claim to have worked full time for a Canadian company and it had better be 8 hours a day or else it apparently does not qualify as full time.

So, once you have obtained permanent residence, don't think working abroad for a Canadian company will not jeopardise your residency. Make sure that you comply with the above, or make sure that you do not have any need to travel outside of Canada. In fact, before you consider immigration ensure that you will almost never have to travel out of Canada until you can get citizenship and a passport. 

There are other considerations before you immigrate to Canada, but this pitfall is the insidious one that gets you after the fact, when it's too late to rectify, so beware!