https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/permanent-residence/non-economic-classes/family-class-assessing-sponsor.html
As you can see this is the operational bulletin/manual for assessing family class sponsorship and specifically the sponsor.
The relevant text is:
"A permanent resident residing abroad is
not eligible to submit a family class sponsorship.
A sponsor must be residing in Canada, unless they are a Canadian citizen residing abroad sponsoring a spouse, common-law partner, conjugal partner or dependent child (provided that the dependent child does not have dependent children of their own) [R130(2)].
Sponsors who maintain a principal residence in Canada are not considered to be in violation of residency requirements if they:
- take short holidays or business trips outside Canada on a temporary basis
- have work arrangements that require them to be outside Canada for temporary finite periods of time, but return to live in Canada in between assignments (such as ship crew or seasonal workers)
Persons who do not maintain a principal residence in Canada and who live and work abroad and only return to Canada for short visits are not considered to meet residency requirements."
You can read and interpret that as you wish. There is no specific definition here of short holidays nor of how precisely they will define "residency." (There are basically two implied hard definitions - "not considered to be in violation of residency requirements" and "not considered to meet residency requirements" - with grey area between them, which is where officers may make an assessment.)
If you're willing to take the risk and/or assess the risk to be low, that's your decision.
They must make an assessment according to the same regs and decide; they certainly can decide to reject on the basis of that assessment. I'm not even clear that they are required to provide a procedural fairness letter (I dont' believe so but not certain), i.e. a sponsor may not have the ability to 'explain' or justify.
Tax payer status or PR status alone are clearly not sufficient - as the regs clearly state, a PR residing abroad is not eligible. (And I'll repeat: there is no clear definition of how 'residing abroad' will be defined or treated, apart from those who maintain principal residence are allowed 'short trips' - which clearly implies that 'long trips' may be treated as not within the intended scope.).
I'd note: you seem confident that you can 'challenge the decision.' Perhaps. Even if an appeal process is allowed (not clear to me), if that is the only reason for refusal, an appeal would likely be far more time consuming and costly than simply re-applying (once back in Canada). (Anyone who has looked at the spouse appeal threads would know the process is long and unpleasant - especially long).
Again, not trying to scare you, just inform you: it's your decision. It's clear enforcement of this is uneven at best - no better info than that is available. If you think two months is fine, that's your call.
Good luck and sorry you've been apart from your spouse and child.