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This does not deny 5+♠. Canape openings will open the shorter suit of a two suited hand, and thus, do not deny a longer suit. This is pre-alertable (in the ACBL at least). However, the 1♥ opening bid is not alerted. It is natural, it shows at least 4-cards, it shows a willingness to play in the suit. The introduction of a SECOND suit, which is confirmed to be no shorter (and usually longer) than the first suit, that bid must be alerted.
Take the sequence: 1♥ - P - 1NT - P - 2♠. 1♥ shows 4+♥. Not alerted. 1NT is usually not-forcing (but still constructive) in Canape systems. 2♠ promises 5+ ♠ (in this sequence). This bid is alerted.
Due to the possibility of a 2♠ bid showing 5+♠, or a 2♣ bid showing 5+♣ (same for diamonds), the pre-alert is necessary to inform your opponents that the unbid suits may not break in a very friendly way, but more importantly, that the team playing Canape will almost certainly have little issue communicating this.