I don't know what the rules are in other places, but permanent roadside memorials aren't allowed in Alberta.
In Calgary, you can put up something for a maximum of a year, and it may be removed by the city before that if it poses a hazard. They also aren't allowed on roads with a speed limit of 70 km/h or higher.
You can get a discreet marker installed on a streetlight location near the site of the incident or have a permanent marker placed on a bench or something nearby.
https://www.calgary.ca/transportatio...memorials.html