You might be able to get France to if the Trent affair happens on a French ship.What would be the most likely intervention scenario?
The US could well have lost the ACW in OTL.
Add British and French support to the CSA and the odds of the North winning drop to zero. Just to start the RN's intervention means the blockade of the CSA is destroyed while the USA is blockaded and cut off from vital resources including nitrates. Lincoln may have a bit of a problem fighting a war without gunpowder.
Didn't Russia threaten to enter the war if Britain or France did? Although, I'm not sure if that was just a bluff.
depends on the level of intervention. If the UK/France just 'recognize' the CSA without any military aid, then the US will shrug and go on about the business of beating the rebels. If the UK intervenes militarily, then the US is going to lose... breaking the blockade against the south and simultaneously blockade the northern ports will break the USA. The USN has a powerful coastal and river force, but nothing to stand up to the RNs ships of the line. The blockade alone is a war winner, but if the UK goes so far as to send troops over, it's just one more nail in the coffin (although land battles are notoriously luck-dependent)...
If memory serves the position of the US is that recognition of the CSA would result in the severing of relations with the UK (and France) and would likely rapidly escalate anyhow.