Region up in Canada is Alberta (4)
I believe the answer is:
asia
'region' is the definition.
(I have seen 'populous region' mean 'asia' so perhaps 'region' could also mean 'asia')
'up in canada is alberta' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'in' indicates the answer is hidden within the clue.
'aisa' is hidden within 'canada is alberta'.
'aisa' back-to-front is 'ASIA'.
(Other definitions for asia that I've seen before include "Great continent" , "Thailand and its location" , "A vast number of people have lived here" , "Eastern continent" , "Stretch of land" .)