All interested in sponsoring their parents or grandparents in 2019 must submit an online application (interest to sponsor) within a timeframe set by the IRCC, and only first 20,000 applicants will receive an Invitation to Apply for immigration. To remind, a lottery (randomized selection of potential sponsors) held in 2017-2018 was cancelled in summer 2018. Starting 2019 all potential sponsors will be selected on a first come, first served basis.
Previous years an online interest to sponsor form was available for sponsors between January 2 and February 1. On December 31, 2018 IRCC made an announcement on Tweeter that in 2019 the program will be opening in late January.