American Express Membership Rewards - Canadian AMEX Platinum Card and Skyteam lounges

I have a Canadian AMEX Platinum card, which lets me in CO, NW, or DL lounges, if I fly those airlines (I presume that the US AMEX Platinum card has a similar benefit?). The question is whether the card will let me in the lounge if I am going on a flight of another Skyteam airline - for example, at MCO, there is a DL lounge, but if I fly a CO flight, will the AMEX card get me in. Of note, the CO flight will not be codeshared on DL nor vice versa.

I have a Canadian AMEX Platinum card, which lets me in CO, NW, or DL lounges, if I fly those airlines (I presume that the US AMEX Platinum card has a similar benefit?). The question is whether the card will let me in the lounge if I am going on a flight of another Skyteam airline - for example, at MCO, there is a DL lounge, but if I fly a CO flight, will the AMEX card get me in. Of note, the CO flight will not be codeshared on DL nor vice versa.
No, it will not. The benefit is the same as the US-based card where you have to be flying on the metal of the carrier that operates the lounge to gain access, except AA, which only requires an AA flight number. At MCO it is further complicated because the DL lounge is behind a different security checkpoint than the CO gates.

While I know the rules are tight about flying on the carrier's metal that operates the lounge, I was surprised recently when my brother with his Plat card was turned away from the NW World Club in MSP because he was flying DL with an NW code-share ticket. If NW is marketing a flight with an NW flight number, I think it is tacky when they turn Plat card travelers away from their lounge for flying on a ticket that they (NW) issued with their flight number on their ticket stock.

While I know the rules are tight about flying on the carrier's metal that operates the lounge, I was surprised recently when my brother with his Plat card was turned away from the NW World Club in MSP because he was flying DL with an NW code-share ticket. If NW is marketing a flight with an NW flight number, I think it is tacky when they turn Plat card travelers away from their lounge for flying on a ticket that they (NW) issued with their flight number on their ticket stock.

It might be "tacky" but the rule is VERY clear. You have to be flying on the metal of the airline that operates the lounge for DL/CO/NW access. AA's policy for access would've gotten your brother in if it were an AA flight number on an AS flight, for example.