With all due respect, you might not think their engagement is canon but I do. They were engaged, even if it was in a different timeline it still counts. Just like how in the mirror box world Jonathan Kent is alive when in the “real world” he’s dead. I should think that any event whether it’s a from a different timeline or in a alternate universe it’s canon. Again with all due respect.
It is not a question of canon or non-canon, but of continuity. It happened in an alternate timeline, erased by time travel. A fiancé/fiancée is not a legal relative. Their engagement ended with the death of that incarnation of Lana (with the one who lives never being engaged to Clark). Maybe some wikis do this sort of thing, but this wikis doesn't list former engagements in alternate timelines in the relatives field.
Nicknames are not aliases. Please don't go in guns blazing questioning people's knowledge; there are multiple reasons to remove information beyond being wrong, and doing this just makes you look like an idiot.
If you looked at the Gideon talk page, you'd see a discussion, which concluded that the Gideons on the two shows have a high probability of not being the same. The reason for this is partly because they're voiced by different actresses (at the same time).