Observation: a failure to satisfy the condition in a conditional PR is not the same as committing marriage fraud.
Conditional PR:
The failure to satisfy a condition will ordinarily result in the loss of PR status, following the appropriate procedure (even though the PR is conditional, the PR is nonetheless still a Canadian and entitled to fair process in any adjudication of the PR's status). Thus, as PMM alludes, the PR must be afforded an opportunity to respond to any claim of having failed to comply with the condition, and among defenses (so-to-say) available to a Condition 51 failure is that there was abuse (including psychogical).
The loss of PR status due to a failure to meet this condition does not result in the inadmissibility of the former PR, just a loss of PR status. Thus, such an individual may remain in Canada, or return to Canada, if that individual qualifies for entry pursuant to some other status. For an American, visitor status is readily obtained and this can allow the individual to spend quite a lot of time in Canada.
Marriage Fraud:
Marriage fraud is not about the breakdown in the relationship after an individual has become a Canadian PR, but about having made misrepresentations of fact in the process of applying for PR, including in particular facts regarding the validity, genuineness, or purpose of the marriage. While marriage fraud is a ground for revoking PR status, as is fraud in applying for PR generally, the process is specifically focused on a charge of inadmissibility. Again, as a Canadian the PR is entitled to the full protections afforded by fair process, but the outcome of this process is (if it determined the individual did indeed make a material misrepresentation in the application) a finding of inadmissibility, resulting in the issuance of a Removal Order (sometimes called a Departure Order) which, at the conclusion of any appeal, becomes enforceable, and which will include the individual being banned from returning to Canada for a period of years.
Procedures generally:
Generally it appears that CIC and CBSA take the report and while the reporting individual may thereafter be further consulted, or otherwise asked to submit additional information, ordinarily the reporting person is not a party to the proceedings, and so will not get any notice of further proceedings or actions taken. I am not certain, but my understanding is that CBSA will ordinarily conduct an investigation into fraud, whereas the failure of a condition proceeding will be conducted by CIC.
Either process can take months to more than a year.
I am not sure of the extent to which even the sponsoring partner is entitled to obtain information from CBSA or CIC regarding the proceedings. There are rather strict privacy limitations on what information either body can divulge to any one other than the subject or the subject's authorized representative.