Forex traders should buy the Canadian dollar, known as the loonie, against the yen as appetite to risk improves, Citigroup has advised.In an investor's note, the banking giant added that the yen may be negatively affected by the political uncertainty currently being witnessed in Japan.The country's prime minister Taro Aso has been forced to defend his position against a disgruntled faction of his Liberal Democratic Party after a vote of no confidence motion was launched.However, the group, led by party secretary general Hidenao Nakagawa, was unable to obtain the 128 signatures necessary to secure the motion.Bloomberg reports that Citigroup responded by advising that the turbulence would "only exacerbate" the short-term prospects for the yen.Meanwhile, the Canadian dollar was touted as one of the world's most undervalued currencies."Since equities, yields and commodities are all tracking higher in the wake of this improvement in sentiment, we suspect that the Canadian dollar may be among the biggest beneficiaries," the group advised.