Prior to America's entry into WWI the Zimmerman Telegram was one incident that helped push America to declare war against Germany and join the Allies, while Mexico never fought against the US was this a possibility? I don't know how strong Mexico was at the time, everything I have read says it was not able to sustain a war of any kind against the US, and considering how far Germany was would there have been any way for Germany to give aid? The telegram seems more a ruse on the US than a way for Germany to incite Mexico to wage war on the US and distract the US from the war in Europe.
It's unclear if you mean whether it was (1) a ruse by Wilson against the American public, or (2) Germany against the USA, or (3) Germany against Mexico, or (4) British against USA?
As far as being a ruse by Wilson (e.g. he made up the telegram to present to Congress), this can likely be discounted since there is documentary evidence - in 2005, an original typescript of the deciphered telegram (with Blinker Hall's handwriting) was discovered in UK.
Also, as noted below, Zimmerman himself admitted to sending it.
As far as Germany's ruse against the USA, it was most definitely not a ruse. It would have had (as it did) an obviously opposite effect of what Germany wanted had it been intercepted - e.g. USA entering the war against Germany on the side of Entente.
In addition, on March 29, 1917, Zimmermann gave a speech in which he admitted the telegram was genuine. (src: Meyer, Michael C. "The Mexican-German Conspiracy of 1915", The Americas. 23.1 (1966): 76)
As far as German ruse against Mexico (in other words, bait them with German help to attack the USA but know all along that you can't provide enough help) - it is certainly plausible, but impossible to ascertain.
On one hand, that was definitely in German interests, since they were worried that USA would declare war on Germany over unrestrained submarine warfare announcement that was forthcoming.
On the other hand, Germany had plausible reasons to believe that Mexico might be successful.
British ruse against Germany - it wasn't the first attempt to ally with Mexico. From Wiki:
The Telegram was not an isolated case of German-Mexican collaboration, for Germany had long sought to incite a war between Mexico and the U.S., which would have tied down American forces and slowed the export of American arms to the Allies. (src: Friedrich Katz, The Secret War in Mexico: Europe, the United States, and the Mexican Revolution (1984) pp 328-9 )
Germany sent, or tried to send the "Zimmerman telegram" to a Mexican government that basically didn't exist.
The reason was that Mexico was in throes of a "free for all" civil war at the time, which is to say that it was in a state of anarchy.
The reason the Germans thought otherwise was because the most unruly of the four major factions, the one under Pancho Villa, "invaded" the United States, crossing the Rio Grande to escape from the others. The Germans reasoned that the Mexicans were trying to recapture Texas and New Mexico, so they offered "Mexico" Arizona and California as well, all of which Mexico had lost to the United States in the 1830s and 1840s.
America's General John J. "Blackjack" Pershing soon launched a counterattack that pushed Pancho Villa back into Mexico. Then he led American forces that ultimately won the First World War from Germany.
Firstly, the Zimmerman telegram was real and sent, he admitted so himself at a press conference.
Secondly, it was a feint to turn Americas attention away from the war in Europe and towards a possible one against Mexico. Germany feared Americas involvement in the war and wanted to ensure they were more concerned with one closer to home. There was no serious plans from Germany at all to support a war between Mexico and America.
Thirdly, The American government thought the telegram was fake when told about it by the British government and thought it was a ruse being used by the British to involve America in a war most of their population were against.