I played Portage last year -- and was pleasantly surprised. No it isn't Cabot or Highlands, and its conditions won't rival Bell Bay, but it was fun, walkable and has some interesting land and holes. It is unpretentious -- it is simply a good $50 golf course that nicely splits the drive around the top of the Cabot Trail. Heck, Chetticamp even has a Tim Hortons, and you don't see too many of those in that part of Cape Breton!
Depending on where you're coming in -- Sydney or Halifax -- will largely depend on what you play. Either way you'll have to drive by Bell Bay, and I'd say while it isn't the most inspired layout, it is an enjoyable round. It'll be interesting to see how it changes since Ted Stonehouse, director of operations for the past decade+, left this year.
The other course on the island that gets discussed is The Lakes (an awful name, I know). It opened in the past few years and is routed next to a ski hill not far from Sydney. I found the strategies a little weak, but it has some great views of, not surprisingly, the lake. Lots of elevation change and not really walkable, though I'm told some will walk it.
I'd pass on Dundee. If I had 10 rounds, I'd do four each at Highlands and Cabot and one at Portage and Bell Bay just to break up drives.