This took two seconds to read:
"
Exception
(4) No person commits an offence under subsection (3) if
(a)
they consumed the drug or the alcohol or both after ceasing to operate a motor vehicle or vessel, or after ceasing to operate or assist in the operation of an aircraft or railway equipment or after ceasing to have the care or control of a motor vehicle, a vessel, an aircraft or railway equipment; and
(b)
after ceasing the activities described in paragraph (a), they had no reasonable expectation that they would be required to provide a sample of a bodily substance."
http://www.parl.ca/DocumentViewer/en/42-1/bill/C-46/royal-assent
Ffs....
Indeed. This does not address what happens if they decide to confront you in the first place just because they want to, and then "catch" you at something else.
And incidentally, at that link, I also read,
"(3) The portion of subsection 254(2) of the Act before paragraph (a) is replaced by the following:
Testing for presence of alcohol or a drug
(2) If a peace officer has reasonable grounds to suspect that a person has alcohol or a drug in their body and that the person has, within the preceding three hours, operated a motor vehicle or vessel, operated or assisted in the operation of an aircraft or railway equipment or had the care or control of a motor vehicle, a vessel, an aircraft or railway equipment, the peace officer may, by demand, require the person to comply with the requirements of either or both of paragraphs (a) and (c), in the case of a drug, or with the requirements of either or both of paragraphs (a) and (b), in the case of alcohol:
(4) Subsection 254(2) of the Act is amended by striking out “and” at the end of paragraph (a), by adding “and” at the end of paragraph (b) and by adding the following after paragraph (b):
(c) to forthwith provide a sample of a bodily substance that, in the peace officer’s opinion, is necessary to enable a proper analysis to be made by means of approved drug screening equipment and to accompany the peace officer for that purpose."
I don't know where the "2 hours after" is coming from when in fact it's anytime within the past 3.