I'm new to this thread, and very interested in the case.
I wish we did have DNA testing for ethnicity, as I think that would narrow things down.
Some of my initial observations:
His clothes are brand name (Levi's, Tims), good quality (real leather belt) and in good condition. I don't think he could have obtained clothes like this if he didn't, at least at some point, have a reasonably well-paying job. He also had orthodontic work. This to me points to a middle-class life at some point in the recent past, and likely a middle-class upbringing as orthodontic work is usually done in one's youth.
If he did get the name from Joyce Carol Oates, he is educated and literate. His tidy handwriting points to this as well. Another indicator of a fairly stable life.
I do think he looks Hispanic or Native, especially in profile. His height seems Native to me, many Cree in that area are quite tall. But his thick eyebrows seem more Hispanic or Eastern European. So I'm going back and forth on that. From the front, he does look Serbian, which matches the last name. There's a large Serbian community in Calgary.
He had to have taken money out from an ATM at some point, or at least gone to a bank, because he had mostly 20 dollar bills. So at some point, he had a bank card or similar identification. Could he have been throwing out these items when he was seen wandering along the highway?
The way he writes his last name looks casual to me, the way the letters are joined seems like he's written it many times before. I wouldn't discount a Lyle Stevic who has simply not been reported missing.