Fill a pot (which will be large enough to submerge all the crab legs) with water, bring to a boil, and add vinegar, coriander, mustard seed, chiles, peppercorns and salt. Cook the crab legs until they turn bright pinkish orange, about 15 to 20 minutes. Remove and let cool until easy to handle.
While the crab is cooling, make the sauce. Combine orange juice, soy sauce, teriyaki sauce, rice vinegar, tomato paste, chile, and ginger root in a small saucepan over medium heat and let reduce by half. Remove from heat and whisk in honey.
Break crab meat from the shell.
To make tempura, mix flour, cornstarch, and baking powder in a bowl. Dredge the crab pieces in this dry mix, shaking any excess back into the bowl. Then add seltzer to the flour mixture in a stream while whisking constantly to make it into batter. Season with salt and pepper.
Heat canola oil to 375 degrees F in a deep fryer, or according to the manufacturer's instructions for similar foods. Dip each piece of crab in the batter, and add the to deep-fryer basket. Fry until golden brown. Drain on paper toweling and serve warm.