You can explain situation adding a letter and indicate he will not come to Canada with her but need to count as a family member for MNI purpose except last sentence of below paragraph.
Note: In the case of a principal applicant who is separated from their spouse, the principal applicant’s separated spouse is considered a “family member”, as per paragraph
R1(3)(a) of the Immigration and Refugee Protection Regulations, since they are still legally married until they are divorced. However, it should be noted that there could be situations in which subparagraph
R5(b)(ii), which details excluded relationships, applies to a foreign national (i.e. the principal applicant). A separated spouse of a foreign national must be counted for the calculation of the Minimum Necessary Income (MNI)
unless the spouse has lived separate from the foreign national for at least one year
and is the common-law partner of another person. For clarity, either the foreign national (i.e. the principal applicant) or their separated spouse may be the common-law partner of another person.