Employment law, absolutely work with a Canadian lawyer. But for filing a patent, it may be better to work with a US law firm.
I once received what I deemed to be very good advice: a patent is worthless if you cannot afford to defend it. So you should file with a company that would be willing to defend your patent on contingency, if they feel there is a good chance of winning. A good law firm recognizes that they'll make a few thousand on margin from the filing of the patent, but they can make millions from defending the patent, taking a 30% cut of the winnings.
Hint: this is generally not the case with Canadian firms, and is far more common in the US. Usually the best bang for your buck is in the top 10-12 of IP law firms. Above that, you probably can't afford them. I prefer to work with a lawyer who is also an engineer and who has a successful track record of litigation. Michael Krieger of Kirton & McConkie would fit the bill (I've worked with him in the past), but he certainly shouldn't have a monopoly on your attention. There are a wealth of lawyers and law firms that you could interview.