According to this page:
https://www.gsmarena.com/google_pixel_3-9256.php
Pixel 3: 1080 x 2160 pixels, 18:9 ratio (~443 ppi density)
UserAgent: Mozilla/5.0 (Linux; Android 9; Pixel 3 Build/PQ1A.190105.004; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/72.0.3626.105 Mobile Safari/537.36 GSA/9.21.5.21.arm64
I got it from my phone, not sure how different the Pixel XL 3 user agent is, but the rest you should be able to get.