Not surprisingly, it didn't take the folks at iFixit to take a scalpel to both the Pixel 3a and the Pixel 3a XL, and thankfully, both have modular components that are more readily accessible for replacement in case of failure.
Unlike most smartphone which feature bodies made out of a combination of aluminum and glass, the new Pixel devices feature plastic bodies. This makes them both lighter and cheaper to produce. It also means that getting inside the devices doesn't require dealing with microwaveable heating pads or heat guns. Instead, the display is held in place with "easily-separated adhesive secures". However, the incredibly easy points of entry also mean that neither phone is IP rated for water/dust resistance.
Components like the 3.5mm headphone jack and USB-port are readily accessible and replaceable. Likewise, the battery is held in place with the same stretchy adhesives as the display in case you need to replace it down the road.
iFixit for the most part was impressed with the repairability of the Pixel 3a and Pixel 3a XL, save for the numerous thin ribbon cables that snake throughout the internal structure of phones and can be easily damaged by clumsy fingers. With that being said, iFixit gave the Pixel 3a and Pixel 3a XL a repairability score of 6 out of 10, which is quite good for a modern smartphone.