For completeness, here is section 185 (it was referenced in the blurb above):
"
Specific conditions
185 An officer may impose, vary or cancel the following specific conditions on a temporary resident:
(a) the period authorized for their stay;
(b) the work that they are permitted to engage in, or are prohibited from engaging in, in Canada, including
(i) the type of work,
(ii) the employer,
(iii) the location of the work,
(iv) the times and periods of the work, and
(v) in the case of a member of a crew, the period within which they must join the means of transportation;
(c) the studies that they are permitted to engage in, or are prohibited from engaging in, in Canada, including
(i) the type of studies or course,
(ii) the educational institution,
(iii) the location of the studies, and
(iv) the times and periods of the studies;
(d) the area within which they are permitted to travel or are prohibited from travelling in Canada; and
(e) the times and places at which they must report for
(i) medical examination, surveillance or treatment, or
(ii) the presentation of evidence of compliance with applicable conditions.
"
And here is the (strikingly similar to ROS, sans the contravention of 185(a)) Extend your stay:
"
Applications for Extension of Authorization to Remain in Canada as a Temporary Resident
Circumstances
181 (1) A foreign national may apply for an extension of their authorization to remain in Canada as a temporary resident if
(a) the application is made by the end of the period authorized for their stay; and
(b) they have complied with all conditions imposed on their entry into Canada.
Extension
(2) An officer shall extend the foreign national's authorization to remain in Canada as a temporary resident if, following an examination, it is established that the foreign national continues to meet the requirements of section 179.
"
So, I still don't see anything about the person being considered "illegal" -- considering there is a remedy for contravention of 185(a), and the application to extend (s.181) is nearly mirrored to the ROS. Sorry, I don't believe that the person would be "illegal" within the 90 day period directly following their validity period.