Your result
Portugal — Marriage
Possible
Everything here turns on one fact, and a single document settles it.
The route requires a spouse who is a Portuguese citizen. Being Portuguese by descent, being from Portugal, having been born in a place Portugal once governed, and holding a Portuguese residence card are four different things, and only citizenship counts.
What settles it: a Portuguese passport, a cartão de cidadão, or an entry in the Portuguese civil register. The register is the definitive one, and the central registry in Lisbon can confirm whether a person is registered. A foreign document that records "Portuguese" as an ethnicity or origin proves nothing.
If they are Portuguese, your route is three years of marriage and a declaration you can make at a consulate — no residence in Portugal needed. If they are not, the question becomes whether they could be: a Portuguese parent or grandparent may give them a claim they have never used, and if they make it, yours follows three years after the marriage date, not three years after their registration.
If neither of you has a Portuguese link, the honest answer is that your route is residence — seven years for nationals of Portuguese-speaking countries and of EU states, ten for everyone else.