A sample Declaration of Legal Representative form is found here.
An applicant for a patent in Canada who is not the inventor must file a declaration to the effect that the applicant is entitled to apply because it is the ‘legal representative’ of the inventor.
The language is confusing, but the intent is not: the applicant is entitled to apply for a patent if the applicant is the successor in title to the inventor.
Provided that it is true, a simple statement, signed by the applicant (or authorized signing officer of the applicant in the case of a corporation) which identifies the inventor and states that the “applicant is the legal representative of the inventor” will meet the requirements.
The definition of legal representative found in the Patent Act is:
“legal representatives” includes heirs, executors, administrators, guardians, curators, tutors, assigns and all other persons claiming through or under applicants for patents and patentees of inventions;
Note that this definition is “inclusive but not exhaustive”.
Of course, in order for the applicant to truly be the successor in title for the Canadian patent application, the applicant should have been assigned all rights to the Canadian patent for the invention by the inventor.
For purposes of Canadian patent law, an assignment should be in writing, signed by the assignee, and witnessed by a third party. Notarization of an assignment is not required for Canadian patent law (Nb: notarization of assignments is often required in other countries, especially civil law jurisdictions).
A sample worldwide invention assignment that is in a form acceptable for filing with the Canadian patent office is found here.