I recieved a DUI in 2006. I have spoken with recruiters from virtually every regional, even interviewed at one. I can tell you that at 2900/130 hours, a bachelors degree, no checkride failures, and being a jet mechanic in the guard, I can not get anyone to hire me. Most of them do not have a problem with the DUI itself since its been 5 years, its not being able to go to Canada that they have the problem with. This must just really mess with their schedules because I've talked to recruiters, chief pilots and even a CEO's and everybodies hands are tied.
Your friends options are:
(1) apply for a temporary resident permit if it is less than 5 years old. This option however is the least likely to result in success, especially since it was recent. A single entry TRP is hard to get, a multiple entry even harder.
(2) after 5 years, apply for crimminal rehabilitation. From what I here this is much easier than the TRP, but can cost any where from 200 to 1000 dollars if you do it yourself.
(3) after 10 years you are considered rehabilitated.

The time starts after the end of your sentence, so if your friend is on probation, he'll have to wait 5 years from the end of his sentence. Keep in mind that once you are elegible to apply for these, there is a lot of leg work, ie police certificates from every city you've lived in since 18. And once you do submit the paperwork it can take them a while to process it. I just recieved a letter from the Canadian consulate in Seattle and they said their processing times are for criminal rehabilitation is 3 years.

All the information is on the Canadian government website under criminal inadmisability. Of course if you have anymore questions you can let me know.

I was fortunate to land a CFI job with a company that actually pays good in 2008 right before things went south. I've been there 3 and 1/2 years and since my 5 years won't be up until Jun 2012, I'm trying to get on with a part 135 company to build my turbine time, and getting my ATP/737 type in february. With any luck in two years I'll have the minimums to apply for the majors and the Canada issue resolved. Yes I am well aware the majors are a long shot but if they won't take me, a regional will. Anyhow my point is you might need to come up with a plan like that.

I have recieved job offers from two airlines that fly EAS routes, and at least three regionals have told me to contact them as soon as I recieve the Canada waiver. If you want it bad enough, there is a chance you can make it, but it will take a while.