go read on the ircc websiteAnyone with a valid study permit who can prove their presence is "essential" can already travel. We do not yet have the finer details of any change in rules such as dropping of the 18th March rule.
"This change to travel restrictions affects all international students, regardless of where they are travelling from or when their study permit was approved."
"The travel of asymptomatic international students who have the appropriate documents to enter Canada and whose DLI is on the list of institutions with approved COVID-19 readiness plans in place will be considered to be non-discretionary and non-optional, unless there is evidence that they are clearly coming to Canada for a discretionary or optional purpose, such as tourism."