Helen,
Even if John Maxwell Brew wrote a will before leaving the IOM it would be listed under the date of probate [after his death], and could be in the IOM if he had property there - otherwise it would be in the country where he died.

It doesn't look as though the family had property in the IOM [from censuses], so the will would probably be found in Canadian records.

Regarding your not being able to find anything about his father Samuel's death, Samuel died between 1861, and 1871 [when his wife was a widow], and not in the IOM.

Elizabeth gave you a possible/probable reference for his death, in England:

Deaths Mar 1865: BREW Samuel [District] Nth Derby [Vol.] 8b [page] 480.

The death cert should give you name(s), date, place, age, cause of death, occupation of the deceased, residence if different from the place of death, and the name and address of the informant [which can be crucial information].

To order the cert see:
http://www.gro.gov.uk/gro/content/certificate/index.asp#0

Sue