There is no limit, if you have even been refused a visa, it has to be disclosed.
All your visa refusals should be declared in your application, not doing so can lead to misrepresentation. As per law you have an obligation to be truthful. Section 16(1) of the IRPA states:
- 16 (1) A person who makes an application must answer truthfully all questions put to them for the purpose of the examination and must produce a visa and all relevant evidence and documents that the officer reasonably requires.
See Tuiran v. Canada (Citizenship and Immigration), 2018 FC 324 (CanLII), <
http://canlii.ca/t/hr59k
Alalami v. Canada (Citizenship and Immigration), 2018 FC 328 (CanLII), <
http://canlii.ca/t/hr6r1>
If you inadvertently missed declaring your prior visa refusal or are unaware of an application for visa you filed, you can list it in your LoE and explain.