Even if he pleaded guilty, how much jail time would he get?
The worst is a life sentence for impaired driving causing death, but that would be saved for the worst kind of offender with the worst previous criminal and driving history.
Given the body count and his being legally over the limit this guy is going to jail if convicted. The only question is, how long?
This guy apparently has no prior criminal convictions on his record, so the aggravating factors to be taken into account, aside from the victim count, would be his previous driving record, the degree of impairment over the legal limit, and the nature of his driving at the time of crash.
Assuming a decent driving record, not driving like a complete lunatic before the crash, and a guilty plea that showed remorse, if he was just a hair over the legal limit in which case the judge could opt go on the low end of jail sentencing, maybe 5 years give or take given the gravity of the outcome, and a driving suspension to match.
On the other hand if he was, like a Halton Hills woman last week, nearly 5 times over the limit, he could be looking at 10 years and a much longer driving suspension.
See
https://canadasafetycouncil.org/sites/default/files/PDF_en/sentencing_in_impaired_driving_cases.pdf for a discussion on various sentences and sentencing principles.
Google up Jonathan Pratt as well, for his sentence when he ran into another car killing 3. Eight years in prison, but his act was aggravated by his speeding (199 kmph) and his BAC being in the high .200 to .244 range. As well, his not guilty pleas and a defence suggesting that another person was behind the wheel at the time probably did little to suggest him showing remorse and taking responsibility for his acts.