Pantalon is a masculine noun. This means you would use "le" before it (e.g., "le pantalon") and the masculine plural form (e.g., "les pantalons").
It's interesting to note that while "pantalon" itself is masculine, the word "culotte", which can also mean pants (though often used for women's pants, like leggings), is feminine.
So, the gender of the word for pants in French is not necessarily tied to its association with a specific gender.