In general, it is considered poor etiquette to simultaneously crosspost an identical question to several sites in the SE network.
There are enough people that peruse multiple sites that it's likely to get noticed rather quickly. Some other sites are much quicker at closing such questions, and you may risk (at times, heavy) downvoting for this behavior on those sites. Such downvoting doesn't seem to happen here on stats.SE, though, as far as I can recall.
In lieu of crossposting, it is preferable to pick the one site that best matches the scope of the question. If you don't get a satisfactory answer after some time (say, a few days), you can flag it and have it migrated to a different site.
If you ask different, but closely related, questions on multiple sites, I would suggest you provide links in each question to each of the other question(s).
You might also look at the following question on meta.SO, which seems to be the quasi-official site-wide policy on this topic: Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?