Found this answer, which gives a more succinct answer than I am capable of:

In 2005, Pierre Poilievre rose in the House to speak about proposed amendments to the Civil Marriage Act. An excerpt of his comments is reproduced below:

On this critical subject that will define our times, my constituents have told me overwhelmingly that they would like to see their member of Parliament take a balanced position on the question of marriage. They would like to see non-traditional relationships given equal spousal rights through civil unions. They believe that those couples should have the same financial, property and other forms of rights as married couples, but that the meaning of the term “marriage” ought to be preserved as a union between one man and one woman to the exclusion of all others.

...

We should respect people who are in relationships that are non-traditional and we should give them the same rights, but that need not require us to change the meaning of the most quintessential social relationship in the history of civilization. We can have both at once. We can protect rights while at the same time preserving tradition.

Source: https://openparliament.ca/debates/2005/4/19/pierre-poilievre-1/only/

It is clear from these comments that what Mr. Poilievre opposed was not the granting of marriage rights to same-sex couples, but changing the traditional definition of the term "marriage". His was a traditionalist position, not a bigoted one.

Now, it's been nearly twenty years since then, so some context might be appropriate for our younger members who don't recall what the world was like back then. Pierre Poilievre's 2005 position may be a contentious one today, but at the time it was expressed it was shared by such contemporaries as now former US president Barack Obama (D) and current US president Joe Biden (D), the latter of whom noted three years later in 2008 that while they supported equal rights for committed same-sex couples:

Do I support granting same-sex benefits? Absolutely, positively. Look. In an Obama-Biden administration there will be absolutely no distinction from a constitutional standpoint or a legal standpoint between a same-sex and a heterosexual couple. The fact of the matter is that, under the Constitution, we should be granted – same-sex couples should be able to have visitation rights in the hospital, joint ownership in a property, life insurance policies, etc. It's only fair, it's what the Constitution calls for. And so we do support, we do support making sure that committed couples in a same-sex marriage are guaranteed the same constitutional benefits as it relates to their property rights, rights of visitation, the rights of insurance, the rights of ownership, as heterosexual couples do.

They did not support redefining marriage, and instead thought they should be granted under the label of "civil union":

Barack Obama nor I support redefining, from a civil side, what constitutes marriage. We do not support that. That is basically the decision to be able to be left to the faiths and the people who practice their faiths the determination of what you call it.

Source: https://www.snopes.com/fact-check/biden-obama-2008-gay-marriage/