“As the Ontario Court of Appeal set out in Westerhoff v. Gee Estate, 2015 ONCA 206, there are different types of experts who are able to offer opinion evidence. They include litigation experts, participation experts and third-party experts. Third-party experts are irrelevant to my consideration in this case.
Litigation experts are, as Simmons J.A. wrote for the court, “engaged by or on behalf of a party to provide [opinion] evidence in relation to a proceeding” (para. 6). They are required to certify their obligations to the court with a Form 20.1 certificate. Participation experts are what Simmons J.A. described at para. 6 as “witnesses with special expertise who give opinion evidence …who form opinions based on their participation in the underlying events.” That group includes treating physicians. That group does not have to sign a Form 20.1 certificate.”
Robinson v. Robinson, 2020 ONSC 7533 (CanLII) at 10-11