If one did not have a job/income for 3 years (and wasn't taking care of one's kids), then how would they prove their physical presence in Canada for citizenship ? or even PR renewal purposes ?
If asked, the onus is on the applicant to prove that s/he physically resided in Canada.
1. Passports can be used as proof (though some countries don't stamp passports on entry/exit).
2. You can provide your rent receipts / mortgage documents because you must have lived in an apartment/house while in Canada.
3. You can provide your provincial health summary (this is the list of all health services you availed using your health card like doctor's visits etc)
Most importantly, there's the CBSA record of your travels. While CBSA only started collecting information about people exiting Canada since June 2020, they have all the records of people entering Canada for a long time now. So, IRCC can directly verify a part of your story by looking at the CBSA records. You could be asked to provide entry/exit records from the countries you've visited (for example, they could ask you to produce I-94 that shows all your entry and exits from the US.