The leading decision on the matter is McLellan Properties LTD v. Roberge 1947 SCR 561 at 566 – 567:

The general rule that one who accepts the position of trustee undertakes to perform personally those duties requiring the exercise of his discretion is subject to certain exceptions. A trustee by the terms of his appointment may be permitted to delegate some or all of those duties. Again, if in the circumstances it would be regarded as prudent for a person in the ordinary course of business to delegate the performance of those duties, a trustee is permitted to do so: Speight v. Gaunt [(1883), 22 Ch.D. 727 (C.A.)]….

These authorities illustrate the general rule and the exceptions thereto founded upon the necessities of prudent business management…

In Re Hatfield Estate (1986), 5 B.C.L.R. (2d) 297 (C.A.), the Court held that trustees may not delegate a power involving the exercise of personal discretion unless they have the authority to do so (see discussion in 0847395 B.C. Ltd. v. Guilbride Estate 2009 BCSC 847 at paras. 64-69; see also Haughton v. Haughton Estate (1995), 80 O.A.C. 273 (C.A.)).

According to Eileen E. Gillese in The Law of Trusts, 3d ed. (Toronto: Irwin Law, 2014) at 160:

If delegation is permitted, trustees may use agents, but they are still responsible for making all decisions. In other words, ultimate decision making rests with the trustees; all they are entitled to do is have the particular agent perform a particular duty or give advice. Trustees, while permitted to delegate some of their duties, may not delegate all of them since that would amount to an abdication of responsibility.