It should not matter at all if you are staying in Canada on a work permit. It will give you an added option for your application. You can apply outland through Buffalo as well as through your country of nationality.
If you have been living together for 12 or more months and can prove it, you are considered a common law couple in Canada and can apply for sponsorship before/without getting married.
If you go for the inland option, you can apply for an open work permit to be granted at your first stage approval (6 months if all goes well) although if you apply outland, you will probably have your PR in 6 months already.
Mr.Leon thanks for your valuable and helpful responses.
Actually i am getting married in April 2010 and planning to apply PR outland in May2010. Can i apply for Open Workpermit visa now i.e before my marriage ??? I am a Permanent Employee in my home country now.
As I said, if you apply inland, you can apply for an open work permit although it will probably take the same amount of time to get one as it would to get the actual PR with outland.
There is no open work permit available for outland.
Open work permits are only given in certain cases, for example, you are applying inland as a spouse or a live-in caregiver and have already gotten first stage approval. Same may be given for refugees.
There is an open post-grad work permit available for people who have studied in Canada.
There are some working holiday open work permits available for a year or two for citizens of certain countries of certain ages.
It is also possible to get an open work permit if you are accompanying a spouse who is on a skilled work permit or study visa but it is not granted to spouses of PR's or citizens as they are expected to sponsor their spouses for PR.
Thank You Leon. 
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