there is a family tree online suggesting manitoba as birthplace you might want to post on manitoba general location to see if anyone is tracking this tree
the william mackay is very familar to me i might have to check my family tree i know i have some mackay's but i don't know about cusitar
also check this link:
http://www.isc.ca/VitalStatistics/Genealogy/vsgs_srch.aspxalso this one:
http://vitalstats.gov.mb.ca/Query.phptype in the last name and see what comes up one is for sask. & the other manitoba
hope this helps