Depending on if there are stopovers (usually 1) and and where they are.. delay times and whatnot.. I've seen that it's generally between 18 and 22 hours.
7 hours
At the time of answering this question (13th November 2013) there are no Virgin Atlantic flights currently flying between Montreal and London (both Heathrow and Gatwick).
The flight time from Pittsburgh, Pennsylvania to Montreal, Canada is about 57 minutes.
The flight time between London and Montreal is approximately 7 hours.
The flying time between London and India (Goa) is 12 hours approx.
The flight time from Montreal, Canada to Casablanca, Morocco is about 7 hours, 2 minutes.
9 Hours
A typical flight between Washington, DC and Montreal, Canada would have a flying time of about 59 minutes.
approx 2.5 hours
Around 90 min.
14
The flight time from London, United Kingdom to Stuttgart, Germany is about 54 minutes.