I didn't really think of the Porter as a backpack. I thought of it more as a suitcase with straps. The lack of a frame is not an issue. I didn't notice that at all (and I've had framed packs in the past). The reasons I picked the Porter were: 1) doing lots of trains and stairs and cobbles, so wheels wouldn't be very useful 2)wheels would take up space that I could use for items 3)the Porter was lighter than the Waypoint.
I looked at the MEC website when I saw you were in Canada. Yeah, they didn't have the Osprey. While you're there, checkout their own brand of a similar bag if they have one. I'm always impressed with the quality of the MEC products.