Germany guarantees a right by law to use the router you want, regardless of ISP [pdf]
dip21.bundestag.de
dip21.bundestag.de
The "endpoint" of the provider's network is now defined as the passive connector at the end of the cable, and providers are required to give their customers all information necessary to configure a connected device, so the customer can choose freely among compatible routers, run non-standard firmware, ...
ISPs regularly send customers routers with known security flaws, already-exposed backdoors that hackers can break into and use laughably weak WiFi security by default (if any at all).
Only Canadian company I've found that let's you have some control on the modem is TekSavvy.
In Belgium, one of the big ISP (can't remember which one) delivered router with open wifi ...
In Spain my ISP only uses the router mac address to 'verify' the equipment.