(See the definition of “eligible individual” in ITA s. 122.6 esp. para. (b) and also the definition in s. 122.6 of "shared custody parent".
In rare cases, you might be able to show that, although the child lives primarily with the other spouse, due to that spouse's work or other reasons, you are the one who gives the primary care. (See paras. 22-25.)
But if your ex-spouse has more custodial days and you pay child support, you may not qualify for the CCTB. See Guerrero c. La Reine, (2013 CCI Favreau), where the TCC said:
" The fact that the appellant's ex-spouse had more custodial days for the child and the fact that the appellant had to pay her a child support allowance tend clearly to show that the mother of the child assumed the primary responsibility for the care and education of the child and that the mother was the eligible individual entitled to receive the CCTB for this period." (My translation.)
See Hrushka v. The Queen, (2013 TCC Woods)