When a SR&ED claim goes to the Tax Court of Canada the standard of proof applied, as in all civil proceedings, is 'balance of probabilities'. This means the claimant only has to show that it's more likely than not that the claim meets the requirements.
A CRA review is not a legal proceeding, and is conducted according to each reviewer's understanding of the SR&ED Directorate's directives. Some RTAs take the view that every element of a claim requires proof 'beyond a reasonable doubt' (which is actually the standard in criminal cases). Others, like the justices in tax court, will accept oral information if the source seems reliable. RTAs are also influenced, some more than others, by reluctance to 'sign off' on any payout of government funds without complete supporting paperwork. Unfortunately, these differencies result in major discrepancies in the review process between one RTA and another.
The standard for SR&ED claim review is supposed to be that the review should be conducted to the extent necessary to support a reasonable level of confidence that there is a minimal risk of material error .