Not sure exactly what you're asking or how this question applies to Canadian immigration but, for the record, I'll record what I know about the difference between CRA and CIC when it comes to common-law status.
CRA and CIC have different criteria for common-law status. With CRA, you are considered common-law partners if you are living together and have a child together, no matter how long you've been living together. CIC says that common-law status comes only after you have co-habitated in a conjugal relationship for a period of at least one year. So, for example, a couple who has lived together for only 8 months, but just had a child together, are considered by CRA to be common-law partners on the date of the child's birth. But CIC would not qualify that couple as common-law partners for purposes of sponsorship, even though they share a child.
I suspect that what you're asking is whether your friend has to declare her partner as a common-law partner for purposes of immigrating, especially since it appears he is applying on his own to immigrate next year. CIC doesn't really care whether a person files single or common-law on their taxes. The applicable question is whether or not the couple has lived together for a period of at least one year - if they have, then she needs to declare him as her common-law partner and he would be assessed for immigration as her partner on her application. That's actually easier than for him to apply to immigrate on his own.
The thing to be careful about is not declaring him as a partner when there's a chance that CIC might consider him to have been her partner before she landed in Canada. Because then (for example, if his own application to immigrate as a FSW, etc., fails) if she tries to sponsor him, they could find him ineligible as a member of the family class because of the relationship prior to her landing. It's actually a lot more difficult to prove that you weren't in a qualifying relationship than that you actually were. Having a child together might cause CIC to assume that there was a qualifying relationship prior to her landing, and exclude him from sponsorship.
The real question: why wouldn't she add him to her own application (if he's eligible) and forget about having him apply on his own next year? In fact, might not be a bad idea to add him - even if he isn't eligible - so that CIC will have the opportunity to assess him. If they find him ineligible as her c/l partner now, then - one day - if he fails in his application as FSW (or however he plans to apply), she could apply to sponsor him and wouldn't run into having to prove that he wasn't a qualified partner when she applied - as he'd already have been assessed for that during her application process.
