Ok, MAGA stands for 'make America great again', got it.
The Quebec mosque shooter apparently will face the criminal justice system and will be punished for taking 6 lives and injuring more. There's actually no need for any protest - this criminal/terrorist will face legal punishment, justice will be done. He'll no doubt receive a lengthy custodial sentence - the longer, the better.
Not so, however, with Khalid Masood. Armed police had to shoot him and then he died in the ambulance. He will never face justice, he'll never be properly punished. The families of the dead and injured will not get justice or any kind of real closure. Something to protest about, perhaps?