First things first: yes, Keanu Reeves is a bit eccentric. And yes, his roles are often surprising and divisive. But he already proved up to the task of portraying a sorcerer with knowledge of the occult in Constantine (2005). For good or ill, when Reeves told audiences that staring into a cat's eyes can pierce the veil between humanity and the supernatural, they took his word for it.
When Keanu fits a role, he fits, and the enigmatic actor has, in many ways, proved to be both as removed and yet kindhearted as Stephen Strange himself, so we have no question he could give a faithful performance. While many other fan-favorites would raise eyebrows or elicit groans from audiences when they began casting 'spells' or 'summoning spirits,' we believe Reeves would seem right at home - that alone makes him an attractive option.