This is not the March for Life. It's the Manif pour Tous protest that took place on January 13th in Paris. I got suspicious because the architecture looked wrong.
This one is in Washington, but no one seems to be protesting. I Googled it and saw that it appeared on Msgr. Pope's blog two days ago, so it's not a post from today's March for Life.
These were posted to show how impressive the March was, but I have not been able to find any good aerial shots of the crowd.