Charlottetown and Fredericton definitely deserve to be on here, though they kind of occupy that awkward space between being a small city and a large town (and for whatever reason, don't seem to have too many peers of their size in Canada).
Now as for some urban towns - Brockville, ON (pop. 22,000) has probably the most muscular downtown of a city that size I've seen in this country. The surrounding housing meanwhile is typical old school, small town Ontario. So, urban, but not too dense.
Stratford, ON (pop. 30,000) meanwhile has a really extensive downtown the size of cities many times its size (like say, Guelph or St. Catherine's), albeit not quite as grand as Brockville's.
Nelson, BC (pop. 10,000) is pretty low-slung aside aside from a few standout landmark buildings, but is also very extensive and impressively vibrant.
Lunenburg, NS (pop. 2,000) doesn't quite have the commercial core of those larger towns, but being an old east coast town it has a nice tightly packed residential fabric.
After awhile, all these towns (at least in Ontario) start to kind of look the same and all have more or less the same form with little appreciable difference in urbanity, but some standouts would nonetheless include the likes of:
Cobourg (18,000)
Port Hope (16,000)
Carleton Place (10,000)