Actually painter is a B skilled profession, see http://www5.hrsdc.gc.ca/NOC/English/NOC/2006/QuickSearch.aspx?val65=painter 7294 Painters and Decorators
If you have enough points to apply for FSW and you have arranged employment, go for it. If you don't have enough points, you might be able to use the arranged employment to apply for your immigration via PNP with your employers support depending on the province.
From other peoples experience, Buffalo will let you apply if you were ever admitted on a 1 year or longer visa, even if you have since become illegal. If that is not the case, you might have to apply through Mexico. If you are not called for an interview, no problem. If you are called for an interview, you would have to go to Mexico. Having been illegal in the US does not affect your immigration to Canada but you would have a very hard time getting a temporary work permit because of it.