Turns out that Edmonton and Hamburg are at nearly exactly the same latitude (around 53° 32' N), as I found out just now when I received a Postcrossing postcard from there. (Postcrossing plots the start and end on a map and draws a line between them, and I wanted to see whether the line just looked horizontal or whether it was actually completely horizontal.)
So the postcard travelled effectively due east all the way! (Well, if it had followed a rhumb line, at least….)
Always fun to see such coincidences.