You could mix Orijen Regional Red with Orijen 6 Fish, or the regular grain-free dog food Orijen has. I've done that before and they didn't have any negative reactions - they're poo was fine and they enjoyed it. However, the 6-Fish made them fart a lot of stinkies (don't know why) so I stopped that one.
I mix in 1 teaspoon of pumpkin in Bella and Sprout's food bowl and 1/2 teaspoon of pumpkin in Gypsy's - every day. It's good for intestinal health and a natural regulator and they like it.
I also like cooking green beans and adding that, but when I do that they dig out all the green beans and throw the actual dog kibble all over the floor in various small piles, so I just do the green bean thing separately as a treat...so they eat their food too.
With regard to Acana versus Orijen, they are made by the same company (as you stated in your post) but there are really a lot of differences between the two:
Orijen and Acana Differences | Naked Dingo Blog
I'm sure whatever you decide to feed Bentley he'll be happy with it!
(We just switched Gypsy from Orijen Puppy to Fromm's Puppy Gold and it's been two days...no problems)