I don't know about the Canadian justice system, but it's very hard in the USA for defendants to get expert witnesses. The state is supposed to pay, but it's almost never done, and when it is they pay bottom rate for the defendant while having unlimited funds for their own experts.
Oh something I can comment on!
A friend of mine was facing a mountain of criminal charges. Photo evidence proved the cops lied. We needed an expert testimony explaining the camera angle and why the photo explained how the cops lied.
I think we called every service qualified for providing such a testimony in Ontario, and a good portion of them across all of Canada. Some were even happy to work with us, until they found out we were testifying against the police. We ended up going international but without luck, and ended up with no expert testimony