what to rotate with Canidae?

You should rotate meat sources, yes. This is so your dog doesn't develop a sensitivity over time. (so the theory goes). Here's some brands that have a variety of different meat sources to choose from:

Wellness 

• Solid Gold
• Taste of the Wild
• Evangers
• Fromm
• etc

This site is good to compare ingredients. You don't need to agree with their ratings - they just list all the ingredients, which is why I find it helpful when switching foods. Keep in mind that this site leans towards no grain, high protein diets. This may or may not be good for every dog.  http://www.dogfoodanalysis.com/dog_food_reviews/ 

How about Nature's Variety Prairie line?  They offer a variety of different formulas ( beef, lamb, venison, salmon, or chicken) and the nutrient profile is similar to that of Canidae (Canidae ALS is 24% protein/14% fat)--the Prairie formulas are all around 26% protein/14% fat----this should minimize the possibility of GI disturbances when you transition.

http://www.naturesvariety.com/content.lasso?page=1476&-session=naturesvariety:4CEE05E30a4182E830HKu15100C5

I second the Nature's Variety Prairie.  Zoe does very well on their beef and rice formula.  A lot of foods give her soft stool but not this one.

I'm rotating Canidae with Fromm 4 Star. (It's also a 5 star food). They have chicken, duck, salmon and whitefish varieties. My dog food guy likes it a lot as the company has very high quality control standards.

I rotate Canidae and NV Prairie formulas. 

I rotate Canidae with NV Prairie as well.  I also use Core ($$$ though) .  I am a big fan of the NV Prairie and they a few different formulas.

How does NV and Fromm compare price wise to Canidae?

 I have used NV kibble samples as treats and the dogs seem to like it (although they like all food!)

Here, it's more expensive.  Canidae is like $35-40 for 40lbs or whatever it is, NV Prairie is like $45 for 35lbs.  Something like that.  It's a little more, and you get a little less.  A lot of people swear by it though, and it's one of few kibble's Kenya's breeder will use besides raw. 

OK, I have narrowed it down to NV Prairie and TOTW for a grain free option (even though it is Diamond).  I checked Fromm and they don't sell it near me now or where I am moving to so it is not a real choice.  I have used the NV as training treats and they like it.  I kinda wanna try a grain free in the rotation to see if it changes anything in them so I may try TOTW too.

Orijen foods are all grain free. I started my puppies on that, and I'm hoping for good results.

Casey eats Blue Buffalo - I rotate the 'flavors' each bag.

I've done TOTW and had good results - however, my dogs coats did not seem as shiny as they were on Canidae. Their poops were better though.

Another option is Innova Evo. I switched my dogs to Evo and feed them half what they were getting on Canidae. So, even though it costs almost twice as much, it works out to be the same. Neiko was eating 4 cups on Canidae and is eating 2 cups (sometimes less) on Evo. Their poops are tiny - hardly anything to speak of and their coats have never looked better.

I've had good results with Orijen (Kibble) however I use Canidae as a topper for my Golden who has skin issues. Haven't had any problems so far!