Austrian Airlines has made this announcement:

Starting late April 2019, Austrian Airlines, Austria’s home carrier will introduce flights to

Montreal throughout the entire year i.e. daily in the summer flight schedule and five times per week in the winter season.

The Star Alliance and joint venture partner Air Canada will assume flights on the Vienna-Toronto route.

The flight connection between Vienna and Toronto will also be bookable as a codeshare flight via Austrian Airlines. Air Canada will begin year-round non-stop service on this route in late April 2019, onboard the Boeing 787-9 Dreamliner. These flights will operate daily in the summer and five times weekly during the winter season. Accordingly, Canada’s largest airline will operate the same number of flights on the Vienna-Toronto route and feature departure and arrival times comparable to Austrian Airlines up until now. 

Montreal and Toronto in the 2019 summer flight schedule 
The duration of the flight from Vienna to Montreal is about nine hours, to Toronto about ten hours. 

Route                      Flight number       Flight days   Departure – Arrival (local times)
Vienna – Montreal   OS 73 (AC 6211)  daily            10:30 a.m. – 1:35 p.m.
Montreal – Vienna   OS 74 (AC 6212)  daily            6:45 p.m. – 8:45 a.m. (next day)

Route                    Flight number        Flight days   Departure – Arrival (local times)
Vienna – Toronto   OS 8247 (AC 899) daily            10:40 a.m. – 1:30 p.m.
Toronto – Vienna   OS 8248 (AC 898) daily            6:25 p.m. – 8:30 a.m. (next day)