In reasons for judgment released last week, the B.C. Court of Appeal in British Columbia v. Canadian Forest Products Ltd., 2018 BCCA 124 summarized the law on causation negligence, saying:
 To summarize, the following principles emerge from the Supreme Court of Canada’s jurisprudence on causation in negligence:
a) The appropriate test for causation is the “but for” test, except in rare circumstances unrelated to this appeal: Clements.
b) Courts must take a common-sense approach to “but for” causation rather than requiring certain or scientific proof of causation: Snell at 328; Clements at para. 9.
c) The burden of proof remains with the plaintiff: Snell at 330. However, as in other fact-finding contexts, a court may infer “but for” causation based on an assessment of all the evidence if the defendant fails to introduce sufficient evidence contrary to the plaintiff’s theory of causation: Clements at paras. 10–11.
d) In determining whether the defendant has introduced sufficient evidence to contradict the plaintiff’s theory of causation, the trier of fact may consider the relative positions of the parties to adduce evidence on causation: Benhaim at para. 54. In other words, evidence should be “weighed according to the proof which it was in the power of one side to have produced and in the power of the other to have contradicted”: Blatch v. Archer (1774), 98 E.R. 969 at 970, cited in Clements at para. 11, Benhaim at para. 48.
e) Even if the defendant’s negligence created causal uncertainty and the plaintiff has adduced some evidence in support of its theory of causation, the trial judge is not obliged to draw an inference of causation against the defendant: Benhaim at para. 42.
f) The trial judge’s decision to infer or not infer causation is a finding of fact and attracts deference on appeal: Benhaim at paras. 36, 42.
The full decision can be found here: http://www.courts.gov.bc.ca/jdb-txt/ca/18/01/2018BCCA0124.htm