Depending on the condition of the adhesive in your Pixel, it might just be very hardened. It takes a lot of consistent and uniform force to open up newer devices.
If your current screen is cracked, try taping over it with packing tape, making sure to leave a single unbroken strip of tape where you'll put your suction cup. Make sure not to tape over the edges of the screen (which would tape the screen shut, making removal even harder). After sufficiently heating the screen, pull on your suction cups with as much force as you can apply without the cup popping off the screen. Keep this pressure for up to a minute. Time is your friend, here. Most adhesives just need time to release.
If your screen isn't cracked, the same techniques will help. When you hold the phone steady, make sure you're not also holding the screen down—just hold the frame by the edges to allow the screen to flex and open.
All in all, nothing surprising is holding your phone together, just the stuck adhesive. Be patient and careful as you work. Post back here with any updates!