Just got my Pixel 3a XL and there is no way to get Boost to activate it. They have all Pixel IMEI blocked, either through internal policy or through orders from Sprint. If a phone works with Sprint it works with Boost, who only piggyback off of the prior. Super disappointed as I've had the same plan for around five years.
I activated Google Fi after an infuriating call with Boost who was no help whatsoever. They even had the audacity to point me to their web store to buy a different phone.
I was on the $80/month plan that included 50GB hotspot data, with Google it's $80/month for unlimited everything.