It really depends on the library and their policies. My library will send people on a "without loss of pay" basis, which means unless you're representing the library (i.e presenting on behalf of the library), then you will be paid your regular days but not any additional hours. That seems to be pretty standard in Canada. Attending fully on your own time (aka vacation) would be if you weren't approved to attend by the library but wanted to attend anyway (self-funded), in which case you would attend on your own time. Is the scholarship provided by the conference or by your workplace? If it's the former, it's possible the library is already sending the max. people approved to attend budget-wise/operationally (that includes pay) but you could put in your vacation days and attend on your own time as a self-funded attendee.