At earliest, May 5th (March 24th parliament comes back, instantly votes no confidence, governor general issues writ the same day, the shortest possible campaign period is 37 days and election day must fall on a Monday).
At latest, Oct 27th (regularly scheduled election is Oct 20th, but that might be delayed by 7 days due to scheduling conflicts - see Bill C-65).
Likely somewhere in between there. All the opposition parties have been signalling that they intend to vote no confidence. Assuming that doesn't change though, there's likely at least a few days lag between parliament coming back, and that happening. The campaign period is likely not to be as short as possible (with an allowable range of 37 to 51 days).
Canadian prime ministers often expire after 10 years for one reason or another
There will likely be an election in 3ish months with a new liberal leader in place of Trudeau