Medical assistance in dying (MAID) is legal in Canada but cannot be accessed through an advance request. Some data suggest that informal care-givers of persons with dementia support the legalisation of advance requests for MAID. Opponents argue that care-givers' support is due to society's failure to address their well-documented burden and unmet needs. To our knowledge, this assumption has never been tested. To fill this knowledge gap, we conducted a survey among 204 Canadian informal care-givers of persons with dementia to (a) elicit their attitudes towards allowing no longer competent adults to access MAID through an advance request, and (b) test the hypothesis that attitudes are in part driven by the level of burden experienced by care-givers and unmet needs for support. Attitudes were elicited with a clinical vignette involving a woman with Alzheimer's disease who requests MAID while still competent, or through an advance request for the time after she would lose decisional capacity. Informal care-givers' support for MAID ranged from 60 per cent in the scenario where the person is still competent and likely has several more years to live, to 87 per cent when she is depicted as no longer competent, in severe distress and close to death. Quality-of-life considerations and the value of self-determination were key arguments in support of legalising advance requests for MAID. Using multivariable logistic regression, we found no evidence that burden and unmet support needs influence attitudes towards advance requests for MAID, after controlling for other determinants. These findings contribute new insights into people's attitudes towards the sensitive issue of whether MAID should be extended to persons with dementia-induced decisional incapacity.